When sugar is mixed with water, equilibrium is reached primarily when the dissolved sugar molecules are evenly distributed throughout the solution. This means that the concentration of sugar is uniform in all parts of the liquid. Even though it may seem like the sugar molecules have settled, they are still in constant motion, moving in and out of solution.
It’s important to note that equilibrium doesn’t mean that the molecules have stopped moving entirely. In reality, the molecules continue to move, but the overall concentration remains stable, which is why it may appear that nothing is happening. So, while the movement of sugar molecules does slow down relative to when they were first mixed in, they never totally stop. Therefore, the correct understanding of equilibrium in this context hinges on the homogeneous distribution of the sugar, rather than a complete cessation of movement.